Study on Morphology and Adult Neurogenesis of hippocampus in Yak

• 1、School of Life Science, Lanzhou University
• 2、 College of Veterinary Medicine, Northwest A &F University

Abstract：Objective The present study explored the morphology and cell types of yak hippocampus, as well as the neural stem cells and newborn neurons located in SGZ of dentate gyrus using histology and immunohistochemistry, providing theoretical basis for both the morphological research of hippocampal formation and adult neurogenesis in dentate gyrus of plateau animals. Methods Fresh yak hippocampal formations were fixed in 4% Paraformaldehyde and Golgi solution, then the traditional H-E staining, Golgi-Cox staining, immunohistochemistry and immunofluorescence labeling against markers for newborn neurons, mature neurons and glias were carried out. The stained sections were observed and photographed using stereoscope, conventional microscope and laser scanning confocal microscope. Results The yak hippcampus mainly consists of dentate gyrus and hippocampus proper, both of them stratify clearly. The granule cells, mossy cells and pyramidal cells are the three major cell types in hippocampus formation. The pyramidal cells in CA3 region are bigger than those in CA1 region, but the average length of apical dendrites of latter are longer. The pyramidal cells in CA1 region are obviously divided into two sublayers rather than form a dense uniform layer like in CA3 region. The pyramidal cells in the inner zone next to hippocampal molecular layer are arranged in cluster, instead, those in the outer zone are distributed loosely. Immunostaining for DCX indicated that adult neurogenesis occurs in yak hippocampus. The somas of most DCX-positive cells are distributed individually or in group in the deepest part of the granular layer close to hilus. Meanwhile, some positive cells are located in hilus or granular layer. The immunofluorescence labeling for GFAP showed that huge number of star GFAP-positive cells scattered in the whole hippocampal formation. Furthermore, the density of GFAP-positive cells in molecular layer, the boundary zone between hilus and granular layer are higher than other layers. Along the subgranular zone of the dentate gyrus, a layer of GFAP-expressing radial glia-like cells located. Their cytoplasms are GFAP-positive while the nuclei are negative, and each soma sent 1or 2 processes to the molecular layer, which are also positive. The terminals of these processes terminated in the granular layer or molecular layer. Conclusion The hippocampal formation of yak has its characters compared with small mammals, such as rat, mouse, cat, rabbit, but is similar to that of sheep. It might be the result of evolution. In addition, the adult neurogenesis existing in yak dentate gyrus seems more powerful because of its unique environment and rigid natural selection.

Keywords： Yak dentate gyrus doublecortin adult neurogenesis